Interactions of nitric oxide-derived reactive nitrogen species with peroxidases and lipoxygenases

The relationship of redox signaling with the risk for atherosclerosis

Oxidative balance plays a pivotal role in physiological homeostasis, and many diseases, particularly age-related conditions, are closely associated with oxidative imbalance. While the strategic role of oxidative regulation in various diseases is well-established, the specific involvement of oxidative stress in atherosclerosis remains elusive. Atherosclerosis is a chronic inflammatory disorder characterized by plaque formation within the arteries. Alterations in the oxidative status of vascular tissues are linked to the onset, progression, and outcome of atherosclerosis. This review examines the role of redox signaling in atherosclerosis, including its impact on risk factors such as dyslipidemia, hyperglycemia, inflammation, and unhealthy lifestyle, along with dysregulation, vascular homeostasis, immune system interaction, and therapeutic considerations. Understanding redox signal transduction and the regulation of redox signaling will offer valuable insights into the pathogenesis of atherosclerosis and guide the development of novel therapeutic strategies.

Structural considerations on lipoxygenase function, inhibition and crosstalk with nitric oxide pathways

Lipoxygenases (LOX) are non-heme iron-containing enzymes that catalyze regio- and stereo-selective dioxygenation of polyunsaturated fatty acids (PUFA). Mammalian LOXs participate in the eicosanoid cascade during the inflammatory response, using preferentially arachidonic acid (AA) as substrate, for the synthesis of leukotrienes (LT) and other oxidized-lipid intermediaries. This review focus on lipoxygenases (LOX) structural and kinetic implications on both catalysis selectivity, as well as the basic and clinical implications of inhibition and interactions with nitric oxide (^•NO) and nitroalkenes pathways. During inflammation ^•NO levels are increasingly favoring the formation of reactive nitrogen species (RNS). ^•NO may act itself as an inhibitor of LOX-mediated lipid oxidation by reacting with lipid peroxyl radicals. Besides, ^•NO may act as an O₂ competitor in the LOX active site, thus displaying a protective role on lipid-peroxidation. Moreover, RNS such as nitrogen dioxide (^•NO₂) may react with lipid-derived species formed during LOX reaction, yielding nitroalkenes (NO₂FA). NO₂FA represents electrophilic compounds that could exert anti-inflammatory actions through the interaction with critical LOX nucleophilic amino acids. We will discuss how nitro-oxidative conditions may limit the availability of common LOX substrates, favoring alternative routes of PUFA metabolization to anti-inflammatory or pro-resolutive pathways.

Oxidative pathways of arachidonic acid as targets for regulation of platelet activation

Platelet activation plays an important role in acute and chronic cardiovascular disease states. Multiple pathways contribute to platelet activation including those dependent upon arachidonic acid. Arachidonic acid is released from the platelet membrane by phospholipase A2 action and is then metabolized in the cytosol by specific arachidonic acid oxidation enzymes including prostaglandin H synthase, 12-lipoxygenase, and cytochrome P450 to produce pro- and anti-inflammatory eicosanoids. This review aims to analyze the role of arachidonic acid oxidation on platelet activation, the enzymes that use it as a substrate associated as novel therapeutics target for antiplatelet drugs.

Inhibition of pacemaker activity in interstitial cells of Cajal by LPS via NF-κB and MAP kinase

AIM: To investigate lipopolysaccharide (LPS) related signal transduction in interstitial cells of Cajal (ICCs) from mouse small intestine.

METHODS: For this study, primary culture of ICCs was prepared from the small intestine of the mouse. LPS was treated to the cells prior to measurement of the membrane currents by using whole-cell patch clamp technique. Immunocytochemistry was used to examine the expression of the proteins in ICCs.

RESULTS: LPS suppressed the pacemaker currents of ICCs and this could be blocked by AH6809, a prostaglandin E2-EP2 receptor antagonist or NG-Nitro-L-arginine Methyl Ester, an inhibitor of nitric oxide (NO) synthase. Toll-like receptor 4, inducible NO synthase or cyclooxygenase-2 immunoreactivity by specific antibodies was detected on ICCs. Catalase (antioxidant agent) had no action on LPS-induced action in ICCs. LPS actions were blocked by nuclear factor κB (NF-κB) inhibitor, actinomycin D (a gene transcription inhibitor), PD 98059 (a p42/44 mitogen-activated protein kinases inhibitor) or SB 203580 [a p38 mitogen-activated protein kinases (MAPK) inhibitor]. SB 203580 also blocked the prostaglandin E2-induced action on pacemaker currents in ICCs but not NO.

CONCLUSION: LPS inhibit the pacemaker currents in ICCs via prostaglandin E2- and NO-dependent mechanism through toll-like receptor 4 and suggest that MAPK and NF-κB are implicated in these actions.

Interaction of the nitric oxide signaling system with the sphingomyelin cycle and peroxidation on transmission of toxic signal of tumor necrosis factor-α in ischemia-reperfusion

This review discusses the functional role of nitric oxide in ischemia-reperfusion injury and mechanisms of signal transduction of apoptosis, which accompanies ischemic damage to organs and tissues. On induction of apoptosis an interaction is observed of the nitric oxide signaling system with the sphingomyelin cycle, which is a source of a proapoptotic agent ceramide. Evidence is presented of an interaction of the sphingomyelin cycle enzymes and ceramide with nitric oxide and enzymes synthesizing nitric oxide. The role of a proinflammatory cytokine TNF-α in apoptosis and ischemia-reperfusion and mechanisms of its cytotoxic action, which involve nitric oxide, the sphingomyelin cycle, and lipid peroxidation are discussed. A comprehensive study of these signaling systems provides insight into the molecular mechanism of apoptosis during ischemia and allows us to consider new approaches for treatment of diseases associated with the activation of apoptosis.

Α-aryl-N-alkyl nitrones, as potential agents for stroke treatment: synthesis, theoretical calculations, antioxidant, anti-inflammatory, neuroprotective, and brain-blood barrier permeability properties

We report the synthesis, theoretical calculations, the antioxidant, anti-inflammatory, and neuroprotective properties, and the ability to cross the blood-brain barrier (BBB) of (Z)-α-aryl and heteroaryl-N-alkyl nitrones as potential agents for stroke treatment. The majority of nitrones compete with DMSO for hydroxyl radicals, and most of them are potent lipoxygenase inhibitors. Cell viability-related (MTT assay) studies clearly showed that nitrones 1-3 and 10 give rise to significant neuroprotection. When compounds 1-11 were tested for necrotic cell death (LDH release test) nitrones 1-3, 6, 7, and 9 proved to be neuroprotective agents. In vitro evaluation of the BBB penetration of selected nitrones 1, 2, 10, and 11 using the PAMPA-BBB assay showed that all of them cross the BBB. Permeable quinoline nitrones 2 and 3 show potent combined antioxidant and neuroprotective properties and, therefore, can be considered as new lead compounds for further development in specific tests for potential stroke treatment.

Redox homeostasis in mycobacteria: the key to tuberculosis control?

Mycobacterium tuberculosis (Mtb) is a metabolically flexible pathogen that has the extraordinary ability to sense and adapt to the continuously changing host environment experienced during decades of persistent infection. Mtb is continually exposed to endogenous reactive oxygen species (ROS) as part of normal aerobic respiration, as well as exogenous ROS and reactive nitrogen species (RNS) generated by the host immune system in response to infection. The magnitude of tuberculosis (TB) disease is further amplified by exposure to xenobiotics from the environment such as cigarette smoke and air pollution, causing disruption of the intracellular prooxidant–antioxidant balance. Both oxidative and reductive stresses induce redox cascades that alter Mtb signal transduction, DNA and RNA synthesis, protein synthesis and antimycobacterial drug resistance. As reviewed in this article, Mtb has evolved specific mechanisms to protect itself against endogenously produced oxidants, as well as defend against host and environmental oxidants and reductants found specifically within the microenvironments of the lung. Maintaining an appropriate redox balance is critical to the clinical outcome because several antimycobacterial prodrugs are only effective upon bioreductive activation. Proper homeostasis of oxido-reductive systems is essential for Mtb survival, persistence and subsequent reactivation. The progress and remaining deficiencies in understanding Mtb redox homeostasis are also discussed.

Convenient synthesis and biological profile of 5-amino-substituted 1,2,4-oxadiazole derivatives

We describe herein a convenient straightforward synthesis of 5-amino-substituted 1,2,4-oxadiazoles, upon the reactions of amidoximes with carbodiimides, as well as their further derivatization to acetamides, in good yields. Most of the compounds exhibited in general low interaction with the stable radical 1,1-diphenyl-2-picryl-hydrazyl. Compounds 32 and 39 inhibited significantly soybean lipoxygenase. Selected compounds were screened for their in vivo anti-inflammatory activity using the carrageenin paw edema model and showed significant anti-inflammatory activity (26, 51%). The ability of the compounds to release NO in the presence of a thiol factor has been also investigated.

Functional and pathological roles of the 12- and 15-lipoxygenases

The 12/15-lipoxygenase enzymes react with fatty acids producing active lipid metabolites that are involved in a number of significant disease states. The latter include type 1 and type 2 diabetes (and associated complications), cardiovascular disease, hypertension, renal disease, and the neurological conditions Alzheimer's disease and Parkinson's disease. A number of elegant studies over the last thirty years have contributed to unraveling the role that lipoxygenases play in chronic inflammation. The development of animal models with targeted gene deletions has led to a better understanding of the role that lipoxygenases play in various conditions. Selective inhibitors of the different lipoxygenase isoforms are an active area of investigation, and will be both an important research tool and a promising therapeutic target for treating a wide spectrum of human diseases.

Specific mediator inhibition by the NO donors SNP and NCX 2057 in the peripheral lung: implications for allergen-induced bronchoconstriction

Background

The aim of this study was to examine potential therapeutic effect of the two NO donors NCX 2057 (3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid) 4-(nitrooxy)butyl ester) and SNP (sodium nitroprusside) on the early allergic airway response in the peripheral lung.

Methods

The experiments were performed in guinea pig lung parenchyma (GPLP) derived from ovalbumin (OVA) sensitized guinea pigs. The effects of NCX 2057 and SNP were evaluated by contractile responses and mediator release during OVA challenge. The generation of nitrite and nitrate was assessed by chemiluminescence. Statistical analysis was evaluated by ANOVA.

Results

Cumulatively increasing concentrations of OVA (1–10,000 ng/ml) induced concentration-dependent contractions of the GPLP that were reduced by NCX 2057 (100 μM, p < 0.001) and SNP (100 μM, p < 0.05). Antigen-induced eicosanoid release was decreased by NCX 2057 (100 μM, p < 0.001) but not by SNP (100 μM), whereas the release of histamine was reduced by SNP (100 μM, p < 0.001) but not by NCX 2057 (100 μM). In addition, NCX 2057 (0.1–100 μM), but not SNP (0.1–100 μM), relaxed leukotriene D₄ (10 nM) precontracted GPLP (p < 0.01). The guanylyl cyclase inhibitor ODQ had no effect on the NCX 2057 mediated relaxation. SNP released significantly less nitrite than NCX 2057.

Conclusion

Although both SNP and NCX 2057 reduced the release of pro-inflammatory mediators, their profiles were distinctly different. Furthermore, NCX 2057 also induced smooth muscle dilation in the GPLP. The findings point to specific anti-inflammatory effects of different NO donors in the peripheral lung tissue.

Life and death: metabolic rate, membrane composition, and life span of animals

Maximum life span differences among animal species exceed life span variation achieved by experimental manipulation by orders of magnitude. The differences in the characteristic maximum life span of species was initially proposed to be due to variation in mass-specific rate of metabolism. This is called the rate-of-living theory of aging and lies at the base of the oxidative-stress theory of aging, currently the most generally accepted explanation of aging. However, the rate-of-living theory of aging while helpful is not completely adequate in explaining the maximum life span. Recently, it has been discovered that the fatty acid composition of cell membranes varies systematically between species, and this underlies the variation in their metabolic rate. When combined with the fact that 1) the products of lipid peroxidation are powerful reactive molecular species, and 2) that fatty acids differ dramatically in their susceptibility to peroxidation, membrane fatty acid composition provides a mechanistic explanation of the variation in maximum life span among animal species. When the connection between metabolic rate and life span was first proposed a century ago, it was not known that membrane composition varies between species. Many of the exceptions to the rate-of-living theory appear explicable when the particular membrane fatty acid composition is considered for each case. Here we review the links between metabolic rate and maximum life span of mammals and birds as well as the linking role of membrane fatty acid composition in determining the maximum life span. The more limited information for ectothermic animals and treatments that extend life span (e.g., caloric restriction) are also reviewed.

Regulation of cytochrome C peroxidase activity by nitric oxide and laser irradiation

Apoptosis can be induced by activation of so-called "death receptors" (extrinsic pathway) or multiple apoptotic factors (intrinsic pathway), which leads to release of cytochrome c from mitochondria. This event is considered to be a point of no return in apoptosis. One of the most important events in the development of apoptosis is the enhancement of cytochrome c peroxidase activity upon its interaction with cardiolipin, which modifies the active center of cytochrome c. In the present work, we have investigated the effects of nitric oxide on the cytochrome c peroxidase activity when cytochrome c is bound to cardiolipin or sodium dodecyl sulfate. We have observed that cytochrome c peroxidase activity, distinctly increased due to the presence of anionic lipids, is completely suppressed by nitric oxide. At the same time, nitrosyl complexes of cytochrome c, produced in the interaction with nitric oxide, demonstrated sensitivity to laser irradiation (441 nm) and were photolyzed during irradiation. This decomposition led to partial restoration of cytochrome c peroxidase activity. Finally, we conclude that nitric oxide and laser irradiation may serve as effective instruments for regulating the peroxidase activity of cytochrome c, and, probably, apoptosis.

Aging in vertebrates, and the effect of caloric restriction: a mitochondrial free radical production-DNA damage mechanism?

Oxygen is toxic to aerobic animals because it is univalently reduced inside cells to oxygen free radicals. Studies dealing with the relationship between oxidative stress and aging in different vertebrate species and in caloric-restricted rodents are discussed in this review. Healthy tissues mainly produce reactive oxygen species (ROS) at mitochondria. These ROS can damage cellular lipids, proteins and, most importantly, DNA. Although antioxidants help to control this oxidative stress in cells in general, they do not decrease the rate of aging, because their concentrations are lower in long- than in short-lived animals and because increasing antioxidant levels does not increase vertebrate maximum longevity. However, long-lived homeothermic vertebrates consistently have lower rates of mitochondrial ROS production and lower levels of steady-state oxidative damage in their mitochondrial DNA than short-lived ones. Caloric-restricted rodents also show lower levels of these two key parameters than controls fed ad libitum. The decrease in mitochondrial ROS generation of the restricted animals has been recently localized at complex I and the mechanism involved is related to the degree of electronic reduction of the complex I ROS generator. Strikingly, the same site and mechanism have been found when comparing a long- with a short-lived animal species. It is suggested that a low rate of mitochondrial ROS generation extends lifespan both in long-lived and in caloric-restricted animals by determining the rate of oxidative attack and accumulation of somatic mutations in mitochondrial DNA.

Nitric oxide deficiency promotes vascular side effects of cyclooxygenase inhibitors

The cardiovascular safety of COX-2 selective and nonselective nonsteroidal anti-inflammatory drugs (NSAIDs) has recently been called into question. The factors that predispose to adverse events by NSAIDs are unknown. Because patients with arthritis have decreased nitric oxide (NO) bioavailability, the in vivo effects of NSAIDs on murine vascular tone and platelet activity in the presence or absence of NO were examined. Here, we show that acute hypertensive and prothrombotic activities of the COX-2-selective inhibitor celecoxib are revealed only after in vivo inhibition of NO generation. The nonselective NSAID indomethacin was hypertensive but antithrombotic when NO was absent. In vitro myography of aortic rings confirmed that vasoconstriction required inhibition of both NOS and COX-2 and was abolished by supplementation with exogenous NO. These data indicate that NO suppresses vascular side effects of NSAIDs, suggesting that risk will be greatest in patients with impaired vascular function associated with decreased NO bioavailability.

Nitric oxide releasing derivatives of tolfenamic acid with anti-inflammatory activity and safe gastrointestinal profile

Tolfenamic acid esters with nitrooxyalcohols are synthesized. They are anti-inflammatory agents reducing carrageenan rat paw edema, with low gastrointestinal and general toxicity. In vitro, they are nitric oxide donors, inhibitors of lipoxygenase and cyclooxygenases. A two to three carbon chain between carboxylic and nitric ester groups seems optimal for activity.

Synergistic antiproliferative and apoptotic effects induced by mixed epidermal growth factor receptor inhibitor ZD1839 and nitric oxide donor in human prostatic cancer cell lines

BACKGROUND

The specific inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase, ZD1839 induces potent antitumoral effects on several advanced cancer types. The present study was undertaken to determine whether the combination of ZD1839 with an agent donating nitric oxide (NO(*)), sodium nitroprusside (SNP) results in a synergy of anticarcinogenic responses on metastatic prostate cancer (PC) cells.

METHODS

The antiproliferative and apoptotic/necrotic effects of ZD1839 and SNP alone or in combination were estimated on EGF- and serum-stimulated LNCaP, DU145, and PC3 cells by MTT growth tests, trypan blue dye exclusion method, and flow cytometric analyses. Moreover, the cellular ceramide levels were evaluated by the diacylglycerol kinase enzymatic method and the amounts of cytosolic cytochrome c by ELISA assays.

RESULTS

ZD1839 and SNP alone or in combination at lower concentrations induced an inhibition of EGF- and serum-stimulated growth of LNCaP, DU145, and PC3 concomitant with an arrest in the G1 phase of cellular cycle. Interestingly, the mixed ZD1839 and SNP also caused a more substantial apoptotic/necrotic death of these PC cells as compared to drugs alone. Moreover, we have observed that an inhibition of acidic sphingomyelinase, hydrogen peroxide (H(2)O(2)) accumulation and caspase cascades results in a significant reduction of apoptotic/necrotic death induced by mixed ZD1839 and SNP in EGF-stimulated PC3 cells. In addition, the combined ZD1839 plus SNP also induced a higher cellular ceramide and reactive oxygen species (ROS) production, mitochondrial transmembrane potential decrease, and cytochrome c amount released into cytosol as compared to drugs alone.

CONCLUSIONS

The simultaneous use of EGFR inhibitor and compound releasing NO(*) might lead to a synergy in the ceramide and ROS production which might cause cellular membrane damages resulting in a massive apoptotic/necrotic death of metastatic PC cells.

In vivo study on cross talk between inducible nitric-oxide synthase and cyclooxygenase in rat gastric mucosa: effect of cyclooxygenase activity on nitric oxide production

The integrity of gastric mucosa during endotoxemia is maintained by the balance of inflammatory mediators, such as prostanoids originated from cyclooxygenase-2 (COX-2) and nitric oxide (NO) from inducible nitric-oxide synthase (iNOS). Thus, we elucidated in vivo cross talk between prostanoids and NO in gastric mucosa during endotoxemia, using an iNOS-specific inhibitor, N-(3-(aminomethyl)benzyl)acetamidine (1400W); a nonspecific COX inhibitor, indomethacin; and a COX-2-specific inhibitor, N-(2-[cyclohexyloxy]-4-nitrophenyl)methanesulfonamide (NS-398). Gastric mucosal NO and prostaglandin E2 (PGE2), a predominant product of COX, expressed as mean +/- S.D. of five rats per group, were assayed by electron paramagnetic resonance spectrometry and enzyme immunoassay technique, respectively. The levels of NO and PGE2 increased gradually up to 6 h after administration of bacterial lipopolysaccharide (LPS) (NO: control, 0.35 +/- 0.16; 6 h, 13.3 +/- 3.3 nmol/g tissue/30 min; and PGE2: control, 288 +/- 16; 6 h, 806 +/- 15 pg/g tissue). Pretreatment with 1400W decreased the increase in NO level without any effect on the PGE2 level (NO, 4.0 +/- 0.4 nmol/g tissue/30 min; PGE2, 788 +/- 26 pg/g tissue). In contrast, treatment with indomethacin and NS-398 inhibited not only PGE2 level but also NO level in a dose-dependent manner without any significant effect on both iNOS and COX protein and mRNA expression. These results demonstrate that in the LPS-treated rat gastric mucosa, PGE2 enhances the release of NO after activation of iNOS, although NO produced by iNOS does not stimulate the release of PGE2 by COXs. The effect of COX activity on iNOS-NO pathway can be important in the regulation of gastric mucosal integrity in inflammatory states.

Enhanced anti-inflammatory potency of a nitric oxide-releasing prednisolone derivative in the rat

1. Derivatization of nonsteroidal anti-inflammatory drugs, such that they release nitric oxide (NO) in small amounts, has been shown to significantly increase their anti-inflammatory activity and analgesic potency. In this study, we compared the anti-inflammatory potency of prednisolone to a nitric oxide-releasing derivative of prednisolone (NCX-1015). 2. Carrageenan-induced inflammation of an airpouch in the rat was used. The rats were pretreated with equimolar doses of prednisolone or NCX-1015 and the effects on leukocyte infiltration into the airpouch and exudates levels of prostaglandin E(2) (PGE(2)), leukotriene B(4) (LTB(4)) and nitrite (as an index of NO production) were measured 6 h later. 3. Injection of carrageenan into the airpouch resulted in a progressive increase in leukocyte infiltration, and accumulation of PGE(2), LTB(4) and nitrite. Carrageenan also induced elevated expression of cyclooxygenase-1 and -2, inducible nitric oxide synthase and 5-lipoxygenase in the inflammatory exudate. 4. Prednisolone dose dependently reduced the numbers of leukocytes within the airpouch exudates, as well as reducing PGE(2), LTB(4) and nitrite levels. NCX-1015 also reduced leukocyte numbers and inflammatory mediator levels. However, the doses of NCX-1015 required to produce a maximal reduction of each of these parameters was one-third to one-tenth the dose of prednisolone that produced a comparable effect. 5. The reduction of PGE(2) and NO production was likely to be at least in part due to reduced expression of the key enzymes responsible for their synthesis (cyclooxygenase-2, inducible NO synthase), with NCX-1015 producing greater suppression than prednisolone at an equimolar dose. 6. Coadministration of prednisolone with a nitric oxide donor (DETA-NONOate) resulted in a greater reduction of leukocyte infiltration and inflammatory mediator production than was observed with either drug alone. 7. These results support the notion that delivery of NO to a site of inflammation can markedly enhance the anti-inflammatory activity of a glucocorticoid.

New advances on structural and biological functions of ceramide in apoptotic/necrotic cell death and cancer

Recent data on the cellular ceramide functions and its involvement in the apoptotic/necrotic cell death as well as its anticarcinogenic properties are presented. The emphasis is on the connections between the ceramide and caspase signaling pathways during the apoptotic cell death process. Notably, the experimental strategies and pharmacological tools used for establishment of the role of ceramide in triggering cell death are described. Moreover, the importance of a compartmentation of endogenous ceramide within the plasma membrane microdomains, lysosomes and mitochondria is discussed. Information on the deregulated functions of ceramide and caspase signaling pathways in several metastatic cancer types is also presented.